Treatiment of acrylonitrile polymer fibers



Aug. 17,1954 L. c. HOLT 2,686,339

TREATMENT OF ACRYLONITRILE POLYMER FIBERS,

Filed OC!;. 4. 1950 JNVENTOR. LA WRENCE C. HOL 7 BY Arron/vi.

Patented Aug. 17, 1954 UNITED STATES PATENT OFFICE TREATMENT OF ACRYLONITRILE PoLY-MER FIBERS ware Application October 4, 1950,.SerialNo,188,306-

( c1. ry -6e) 13 Claims.

Thisinvention relates to the treatmentv of fibers of an acrylonitrile polymer. More particularly, the invention relates to a processfor continuously crimping acrylonitrile polymer fibers which are in an internally strained condition and relaxing the internals strains to thereby reduce the residual shrinkage capacity of the fibers and stabilize them in the crimped condition, in a single operation.

Continuous fibers may be formed from acrylonitrile polymers of suitable molecular weight and containing, in the molecule, at. least '75 percent of acrylonitrile,v by either the wetor dry-spinning process. The freshly formed fibers are not highly oriented and have relatively low tensile strength as compared to highly oriented acrylonitril'e polymer fibers in which the molecules are aligned or oriented inthe direction of the fiber axis. Any treatment or handling of the substantially unoriented or lowly oriented fibers which induces orientation of the molecules to any extent,, as; for example, holding them under tension under conditions such that they are heated, introduces internal strains and leaves the fibers in an internally unbalanced condition in which the continuous fibers, or discontinuous fibers obtained by cutting. or otherwise disrupting the continuous fibers, tend to shrink on subsequent heating, thereof 'to elevated temperatures, in use.

In the conventional practice, the substantially unoriented or lowly oriented acrylonitrile polymer fibersobtainedby extruding a solution of the polymer into a liquidv coagulating bath, or into an atmosphere in which the spinning solvent is evaporated,.are stretched under heating to thereby orient the molecules in the direction ofthe fiber axis and improve the strength of the fibers. Fibers which arestretched and in an internally strained condition have an undesirably high residual shrinkage capacity. This disadvantage may be overcome and undesirable shrinkage of the fibersin use prevented, by heating the internally strained fibers in. a relaxed condition in which they are free to shrink whereby the strains are relieved, and the fibers arestabilized against shrinkage at the temperature of heating. In the conventional practice the heat-stretching for orientation, and. heat-relaxation are performed batch-wisein separate operations, In those instancesin which the continuous fibers have been reduced to staple length, this has usually been accomplished-by cutting the continuous fibers and thenrelaxingthem.

Unlike woo1,-. the acrylonitrile polymer fibers are relatively straight and have a smooth, slick surface and are not adapted to" being spun into a yarn on either the cotton or woolen systems. To facilitate the carding and/or combing and drafting operations to which the discontinuous fibers of the polymers are subjected incidental to spinning them into a yarn, it is essential to crimp them so that they will exhibit sufiicient coherence at least during the early stages of the yarnspinning operation to permit spinning thereof into a yarn on conventional textile processing equipment.

One object of this invention is to provide a method for crimping and relaxing internally strained acrylonitrile polymer fibers in a single operation. Another object is to provide a method for crimping acrylonitrile polymer fibers and stabilizing them inthe crimped condition by relieving internal strains therein while imparting crimp thereto. A further object is to provide a method for producing acrylonitrile polymer'fibers having. a controlled-residual shrinkage capacity and improved textile processing characteristics.

In accordance with the invention, internally strained continuous fibers of an acrylonitrile polymer, which do not contain more than 5 percent of the spinning solvent, and preferably in the form of a' tow" or bundle, are continuously passed between rollers into and through a crimping chamber which is maintained full of fibers and in which the fibers are held in packed condition for a predetermined time while they'are subjected to heat, whereby packing pressure causes them to crimp and the molecular strains are relaxed under the influence of the heat, with stabilization of the fibersin the crimped condition. The crimped continuous-fibers may then be severed to discontinuous lengths by any suitable means, and, if necessary, the crimped staple lengthsare dried. The drying may be performed prior to cuttingor severing-the continuous fibers.

In the preferred embodiment, the crimping chamber is at least as wide as the tow or bundle as it isfedto the chamber, and preferably-the Width of the crimping chamberis the same as the width of the tow as it is fed to the'chamber and the bowis caused to fold-back and forthupon itself in layers,. in which condition it passes to the chamber exit.

While the tow or bundle is in-the packed, folded condition,. it is heated to atemperature determined by the temperature at which the fibers are toremain stable to subsequent objectionable shrinkage in use. The extent of relaxation of the strains in' the'fibersor filaments determines the residual shrinkage capacity of the fibers, and

is a function of the temperature to which the tow is subjected during relaxation of the strains and the duration of the heat-treatment. Generally, for practical purposes, the fibers should be stable to boiling water in use and, therefore, in practicing this invention, the packed tow of acrylonitrile polymer fibers will usually be heated to atemperature of 100 C. or higher, such as 110 to 130 C. for a time to internally relax the fibers to the extent that their residual shrinkage capacity is not greater than 3 percent at 100 C. The heating time will vary depending on the pre vailing conditions, such as the size of the tow, the size of the fibers in the tow, the length of the crimping chamber, and the rate of feed of the tow to and through the chamber, these conditions being selected so that, within the time required for the packed tow to pass from the entrance of the crimping chamber to the exit thereof, the fibers of the tow are internally relaxed to the required extent.

The tow packed in the chamber may be heated to the desired temperature by any suitable heating medium such as hot air or steam, which may be dry, moist, saturated or superheated steam. Dry or superheated steam is preferred, since its use reduces the time required for drying the tow of crimped fibers after it leaves the chamber.

The continuous fibers which are simultaneously crimped and internally relaxed in accordance with this invention are characterized by a pronounced crimpiness and each fiber of the tow or bundle is crimped. The number of crimps per inch can be varied but preferably the packing pressure is such that the crimps occur at closely spaced intervals along the length of the tow. In any case, the crimps tend to lie in a single plane through the tow along considerable distances, but their disposition may frequently swing into other planes at various angles about the length of the tow as an axis. While a gentle sine wave type of crimp may be obtained if the packing pressure is quite light, it is preferable to have a higher packing pressure which will produce a sharpangled or serrated crimp which appears like sawteeth in contour. Discontinuous fibers cut from these crimped and stabilized continuous fibers have improved textile processing characteristics and are particularly suitable for working up on conventional textile working equipment, either alone or in blends with other fibers.

The discontinuous fibers obtained by cutting or otherwise disrupting the crimped tow can be spun into a yarn without further treatment, the carded webs and rovings or slivers comprising them being coherent structures which can be subjected to strong drafting without separation of the fibers.

The continuous acrylonitrile polymer fibers which are crimped and stabilized in crimped condition by internal relaxation, may have any degree of orientation. The fibers may not be oriented to any greater extent than results from handling thereof incident to their production and resulting from their withdrawal from the spinning zone and passage through a washin and conditioning zone, and/or into the crimping chamber. Or they may be positively stretched to any desired extent by stretching them between godets or by means of other thread-handling, thread-stretching devices, while they are heated, preferably by steam. Fibers having the highest degree of orientation, and therefore the highest tensile strength, are obtained by stretching the fibers at least 100% under heating, prior to simultaneously crimping and relaxing them accordance with the invention. In any event, the fibers must not contain more than 5 percent of the spinning solvent when they are passed through the crimping chamber, and preferably contain from zero to 1.5 percentof residual spinning solvent. ihe solvent may be removed from the fibers, or reduced to not more than 5 percent by weight, by washing the fibers thoroughly after their formation.

In one presently preferred embodiment of this invention, the continuous acrylonitrile polymer fibers containing not more than 5 percent spinning solvent by weight, are stretched for orientation, in a heated condition, and passed directly from the stretching stage into and through the crimping chamber in which they are caused to fold back and forth upon themselves and heated in the packed, folded condition, the stretching for orientation and crimping and relaxation bein effected continuously.

The attached drawin illustrates suitable means for carrying out one preferred embodiment of the method of the invention. In the drawing,

Fig. 1 is a front elevation of the apparatus;

Fig. 2 is a plan view of the portion of the apparatus embodying the crimping and relaxing chamber; and

Fig. 3 is a front elevation of the apparatus with parts removed.

Referring to the drawings, the tow 2 of continuous acrylonitrile polymer fibers which have been freed of residual spinning solvent, or which do not contain more than 5 percent of the solvent, is passed from the pair of canted rotors or godets 4, 5, and thence to the canted rotors or odets 6, I, through the stretching tube 8. Steam under pressure or other suitable heating medium is introduced into the tube through the conduit 9 and escapes through the conduit I0. From godets B,

l the tow is fed directly to the crimping device comprising a crimping chamber l2, between the feed rolls l3, M, which preferably have smooth, cylindrical surfaces but for certain fibers or filaments may be corrugated or serrated to varying degrees.

Feed roll I3 is keyed to shaft l5 which is journalled in bearing blocks l6, l1 fixed to a fixed supporting plate l8 and carries a gear I8 and a sprocket 20 which is driven by a chain connected to a suitable power source, not shown. Feed roll I4 is keyed to shaft 2| which is journalled in bearing blocks 22 and 23 and carries a gear 24 meshing with the gear [9. Bearing blocks 22 and 23 are provided with slots 25 and fastened to the plate Is by studs 26. The bearing blocks slide back and forth in the slots, to compensate for any variation in the thickness of the tow passing between the feed rolls. The feed roll [4 is held in pressure engagement with the tow passing between the rolls by a cushion 27 of any suitable resilient material, such as rubber, which bears against the bearing blocks 22 and 23. Resilient member 21 is secured to the threaded rod 28 which is in turn adjustably secured to the lug 29 fixed to the plate l8.

As shown, the crimping and relaxing chamber i2 is formed by the rolls l3, M, a panel 45, a removable cover plate 35, the diverging doctor blades 33, 3| and the downwardly inclined strip 32 which is one arm of a lever pivoted at 32c, the other arm 33 of which terminates in an enlarged portion 34. The removable cover plate 35 may be screwed to the doctor blades which in turn are screwed to the panel 45. The total Weight of 33 and- 34 must be lighter than arm 32. Panel 45 extends at a right angle to plate l8 and is integral with it or fixed thereto.

The doctor blades are preferably formed of highly polished metal and constitute the opposite sides of the chamber. The blades are fixed to the panel 45 in diverging relation, and with their upper ends abutting against rolls l3, [4, below the nip of the rolls, to control the deflection of the tow leaving the nip.

The inclined plate 32 forms a partial bottom closure for the crimping and relaxing chamber I2, to permit continuous discharge of the crimped tow of continuous filaments. As shown, the tow is treated with steam as it passes from the nip of the rolls I3 and M to the restricted exit between the blade 3| and the end of the downwardly inclined plate 32. Steam is introduced into the chamber at a point just below the nip of the rolls l3, l4 through the pipe 33. Optionally, steam may also be introduced into the chamber at a point adjacent the exit from the chamber through the pipe 31.

Although the crimped and stabilized tow is continuously discharged from chamber [2, the exit passage is narrow to cause suificient backpressure to develop in the chamber to insure packing and crimping of the filaments.

Once the operation has been initiated, the chamber is kept full and the tow is fed to the chamber at a rate to insure a packed or stuffed condition. The back-pressure of the fibers packed against strip 32, and the fact that the tow, as fed to the chamber, has a width corresponding to the width of the chamber, causes the tow being forced into the chamber by the feed rolls to fold back and forth upon itself, in layers, and to assume a crimped condition. The crimps occur at fairly regular, closely spaced intervals along the tow length.

The tow is held in the packed condition in the chamber by the strip 32 which remains in position until the pressure exerted on it by the packed tow exceeds a set, predetermined limit. When that happens, plate 34 carrying arm 33 to which the inclined strip 32 is pivotally secured rises against the rod 38 which may be resiliently urged downwardly against enlargement 34, such as by a spring weight, or as shown by fluid pressure in a cylinder 39. When this occurs, strip 32 is lowered and the exit from chamber I2 is widened so that the crimped tow is discharged at a somewhat higher rate, after which strip 32 may return as conditions permit. The cylinder 39 is connected to a hydraulic or pneumatic reservoir by the pipe 40, and the pressure exerted on piston 38a is controlled by the valve Ma in a discharge pipe 4|.

In the embodiment illustrated, the stretching to which the continuous fibers constituting the tow are subjected as they proceed to the feed rolls I3, l4 introduces molecular stresses and strains which tend to be relieved, with shrinkage of the fibers or short fibers cut from them, when the fibers are subsequently subjected to elevated temperature. This tendency of the fibers to shrink must be controlled if undesirable shrinkage of the yarns or fabrics formed from them is to be avoided, and as previously mentioned it has been the practice to heat the stretched fibers, or fibers cut therefrom, in a relaxed condition, in a separate operation, prior to fabricating them.

By the present method, the continuous fibers of the tow may be uniformly stretched for orientation and then uniformly heated and relaxed simultaneously with crimping thereof. Heating of the tow as it leaves the nip of the rolls and while it is in, the packed condition in chamber I2 effects relaxation of the strains introduced, by the stretching and such relaxation reduces the residual shrinkage capacity of the fibers and sets the crimp developed therein by the back pressure in the chamber. The crimped fibers withdrawn from chamber l2 have a residual shrinkage capacity of not more than 3 percent at the temperature to which they are heated in the chamher, which may be any temperature between that at which the acrylonitrile polymer would shrink before the heat-relaxation, and the melting point of the polymer.

Discontinuous fibers cut or otherwise obtained from the crimped tow are characterized by a pronounced crimp and desirably low residual shrinkage capacity. They exhibit improved textile processing characteristics and may be carded and/or combed and spun into a yarn Without further treatment. Because they are crimped and stabilized in the crimped condition by relaxation of the internal strains in the crimping chamber, the fibers can be spun into a yarn without difliculty.

The acrylonitrile polymer fibers may be formed from any fiber-forming acrylonitrile polymer containing, in the molecule, at least percent of acrylonitrile, including polyacrylonitrile, twocomponent copolymers, ternary polymers, and blends of an acrylonitrile polymer with other polymeric materials.

For example, the continuous fibers may be formed from a copolymer of acrylonitrile with one or more copolymerizable substances containing the linkage C=C Examples of suitable copolymers and ternary polymers are those containing, in the molecule, from 75 to 99 percent by weight of acrylonitrile and from 1 to 25 percent by weight of one or more of the following: acids such as acrylic, haloacrylic, and methacrylic acids, esters such as methyl methacrylate, butyl, octyl, methoxymethyl, and chlorethyl methacrylate and the corresponding esters of acrylic and u-chloracrylic acids; methacrylonitrile, vinyl and vinylidene halides such as vinyl chloride, vinyl fluoride, vinylidene chloride, l-fiuoro-l-chlorethylene; vinyl carboxylates such as vinyl acetate, vinyl chloracetate, vinyl propionate, and vinyl stearate; N-vinylimides such as N-vinylphthalimide and N-vinyl succinimide; N-vinyl lactams such as N-vinylcaprolactam and N-vinyl butyrolactam; vinyl aryl compounds such as styrene and vinyl napthalene; and other compounds such as methyl vinyl ketone, chlortrifluorethylene, methyl fumarate, methyl vinyl sulfone, methyl vinyl sulfoxide, methyl vinyl sulfide, fumaronitrile, maleic anhydride, and various isomeric vinylpyridines such as Z-Vinylpyridine, 3- vinylpyridine, and 4-vinylpyridine, and the vinylsubstituted alkyl pyridines such as 4-ethyl-2- vinylpyridine, 5-ethyl-2-vinylpyridine, 4-methyl- 3-vinylpyridine, 5ethyl-3-vinylpyridine, 4,6-dimethyl 2 vinylpyridine, 2-methyl-5-vinylpyridine, and 6-methyl-2-vinylpyridine, the isomeric vinylpyrazines, the various isomeric vinylquinolines, the vinyl oxazoles, the vinyl imidazoles, and the vinyl benzoxazoles.

The continuous fibers or filaments may also be formed from a blend of a base acrylonitrile polymer with other polymeric materials which modify the base polymer in various respects, as by imparting dye-receptivity thereto, increasing the flame-resistance thereof, or increasingthe hydrophilic properties of the polymer, etc. Suitable polymeric materials for blending with the base polymer, which may be polyacrylonitrile or copolymer-s or ternary polymers of acrylonitrile with the copolymerizable substances mentioned above are those polymeric materials which are soluble in dimethylacetamide, and which, when mixed with the base polymer in an amount of from 2 to 50 percent on the weight of the blend, result in a blend which forms a solution of at least percent concentration in dimethylacetamide which solution can be formed into fibers by conventional procedures. Solvents other than dimethylacetamide may be used in forming fibers from these blends.

As an illustration, the blend may comprise a base polymer which is not normally receptive to an acid dye, such as a copolymer containing from 90 to 99 percent by weight of acrylonitrile and from 1 to percent by weight of vinyl acetate with from 2 to 50 percent by weight of a copolymer containing from 10 to 70 percent of acrylonitrile and from 30 to 90 percent of a vinylsubstituted heterocyclic tertiary amine, for example 2-vinylpyridine, or other polymeric material containing basic nitrogen, the blend being receptive to acid dyestuffs.

The acrylonitrile polymers and copolymers from which the fibers are formed may be produced by any suitable polymerization method, including bulk or mass polymerization, solution, emulsion, or suspension polymerization.

Blends may be obtained by mixing the acrylonitrile polymer with the modifying polymeric material in the dry state, without or with a plasticizer, or by dissolving the two materials in a solvent in which they are both soluble or which is a solvent for the blend.

Example Using apparatus as shown in Fig. 1, a bundle of substantially parallelized continuous fibers formed from a dimethylacetamide solution of a copolymer containing, in the molecule, 97 percent of acrylonitrile and 3 percent of vinyl acetate having a total denier of 34,000 and which contained about 2 percent of dimethylacetamide by weight, was passed from the godets 4, 5 into the steam tube 8, to godets 5, '5. Steam under 120 lbs. pressure was introduced into tube 8 and through a partially closed valve arrangement and the tow was stretched 320 percent, as it passed through the tube. The stretched tow leaving godets 6, l was then stuffed into the chamber 12 by the feed rolls I3, 14. The width of chamber l2 was substantially the same as the width of tow 2 as it was fed to the chamber, Dry steam was continuously introduced into the chamber under a pressure of 1 lb. per sq. inch, to heat the tow to a temperature of at least 100 C. The speed of the rolls l3, N5, the dimensions of the chamber l2, and the pressure of air above piston rod 24 were such that each succeeding portion of the tow passing through the chamber was subjected to the steam for an average period of approximately 15 seconds, before it emerged from the chamber. The fibers of the tow discharged from the chamber were crimped and substantially freefrom internal strains. These fibers had a residual shrinkage capacity of about 2 percent at 100 C.

Suitable conditioning agents, for example, lubricating and anti-static agents may be applied 8. to the fibers at any stage between washing thereof or removal of spinning solvent by evaporation, and stufiing of the tow into the crimping chamber, and/or after the tow is discharged from the chamber.

The tow crimped and relaxed as described above was cut to highly crimped, internally relaxed and stabilized short fibers which were mixed with wool fibers and spun into a yarn using conventional spinning apparatus and methods.

A carded web consisting exclusively of acrylonitrile polymer fibers crimped and stabilized as described was a coherent structure which did not separate under the normal stress encountered in spinning a yarn.

Some changes and modifications may be made in practicing the invention without departing from the scope of the invention, and therefore the invention is not to be limited except by the appended claims.

I claim:

1. A process for producing crimped, stabilized fibers comprising an acrylonitrile polymer containing, by weight in the polymer molecule, at least 75 percent of acrylonitrile, which comprises continuously passing continuous internally strained fibers comprising the polymer through a zone, heating the fibers in the zone and stretching the fibers in the zone at least percent while they are under the influence of the heat, continuously passing the stretched, oriented fibers from the zone into and through a crimping zone, continuously folding the bundle back and forth upon itself in a packed condition in the crimping zone to thereby crimp the fibers, continuously treating the packed bundle of fibers passing through the crimping zone with steam to thereby heat the fibers to at least 100 C. and relax the internal strains, reduce the residual shrinkage capacity of the fibers to not more than 3 percent at 100 C., and stabilize the relaxed fibers in the crimped condition, and continuously removing the stabilized, crimped fibers from the crimping zone.

2. A process for producing highly oriented, crimped, stabilized fibers comprising an acrylonitrile polymer containing, by weight in the molecule, at least 75 percent of acrylonitrile, and having a low residual shrinkage capacity from substantially straight continuous acrylonitrile polymer fibers having, at most, low orientation, which comprises continuously passing a bundle of substantially parallelized, continuous fibers comprising the polymer through a zone in which it is heated and stretching the bundle at least 100% while it is under the influence of the heat, continuously passing the bundle of stretched, oriented fibers from the stretching zone into and through a second zone, continuously folding the bundle back and forth upon itself in a packed condition in the second zone to thereby crimp the fibers, continuously heating the packed bundle of fibers to a temperature of at least 100 C. to internally relax the fibers, reduce the residual shrinkage capacity of the fibers to not more than 3 percent at 100 C., and stabilize the relaxed fibers in the crimped condition, and continuously removing the stabilized, crimped fibers from the second zone.

3. A process as in claim 1, wherein the fibers comprise a copolymer containing, by weight in the copolymer molecule, from 75 to 99 percent acrylonitrile and from 1 to 25 per cent of at least one other substance which contains the C=C linkage and which is copolymerizable with acrylonitrile.

4. A process as in claim 1, wherein the fibers comprise a blend of an acrylonitrile polymer containing, by weight in the polymer molecule, from 75 to 100 percent of acrylonitrile and from to 25 percent of at least one other substance which contains the C=C linkage and which is copolymerizable with acrylonitrile, with from 2 to 50 percent on the weight of the blend of a modifying polymeric material which is soluble in dimethylacetamide and which, when mixed with the base polymer in an amount of from 2 to 50 percent by weight, results in a blend which forms a solution of at least percent concentration in dimethylacetamide, which solution can be formed into fibers by conventional procedures.

5. A process as in claim 2, wherein the fibers comprise a copolymer containing, by weight in the copolymer molecule, from 75 to 99 percent acrylonitrile and from 1 to 25 percent of at least one other substance which contains the C=C linkage and which is copolymerizable with acrylonitrile.

6. A process as in claim 2, wherein the fibers comprise a blend of an acrylonitrile polymer containing, by weight in the polymer molecule, from 75 to 100 percent of acrylonitrile and from 0 to 25 percent of at least one other substance which contains the C=C linkage and which is copolymerizable with acrylonitrile, with from 2 to 59 percent on the weight of the blend of a modifying polymeric material which is soluble in dimethylacetamide and which, when mixed with the base polymer in an amount of from 2 to 50 percent by weight, results in a blend which forms a solution of at least 5 percent concentration in dimethylacetamide, which solution can be formed into fibers by conventional procedures.

7. A process for producing crimped, stabilized fibers comprising an acrylonitrile polymer containing, by weight in the polymer molecule, at least 75 percent of acrylonitrile, which comprises continuously passing a bundle of continuous substantially parallelized fibers comprising the polymer and having, at most, low orientation, through a zone, heating the fibers in the zone and stretching the fibers in the zone at least 100 percent while they are under the influence of the heat, continuously passing the bundle of stretched, oriented fibers, which are internally strained, into and through a crimping chamber having a width at least equal to the width of the bundle as it is fed to the chamber, continuously folding the bundle back and forth upon itself in a packed condition in the crimping chamber to thereby crimp the fibers, continuously heating the packed fibers passing through the chamber to a temperature of at least 100 C., to thereby internally relax the fibers and stabilize them in the crimped condition, and continuously removing the bundle of stabilized, crimped fibers from the crimping chamber.

8. A process as in claim 7, wherein the fibers are heated with steam.

9. A process as in claim 7, wherein the fibers comprise a copolymer containing, in the copolymer molecule, from 75 to 99 percent of acrylonitrile and from 1 to 25 percent of at least one other substance which contains the C=C linkage and which is copolymerizable with acrylonitrile.

10. A process as in claim 7, wherein the fibers comprise a blend of an acrylonitrile polymer containing, by weight in the polymer molecule, from to 100 percent of acrylonitrile and from 0 to 25 percent of at least one other substance which contains the C=C linkage and which is copolymerizable with acrylonitrile, with from 2 to 50 percent on the weight of the blend of a modifying polymeric material which is soluble in dimethylacetamide and which, when mixed with the base polymer in an amount of from 2 to 50 percent by weight, results in a blend which formsa solution of at least 5 percent concentration in dimethylacetamide, which solution can be formed into fibers by conventional procedures.

11. A process for producing crimped stabilized fibers comprising an acrylonitrile polymer containing, by weight in the polymer molecule, at least of acrylonitrile, which comprises continuously passing continuous internally strained fibers comprising the polymer through a zone, heating the fibers in the zone and stretching the fibers in the zone at least 100% while they are under the influence of the heat, continuousiy passing the stretched, oriented fibers from the zone into and through a crimping zone in a packed condition to thereby crimp the fibers, continuously heating the packed fibers passing through the crimping zone to a temperature below the melting point of the acrylonitrile polymer and above the temperature at which the fibers tend to shrink immediately prior to their introduction into the crimping zone, to thereby internally relax the fibers and stabilize them in the crimped condition, and continuously removing the stabilized, crimped fibers from the crimping zone.

12. A process as in claim 11, wherein the fibers comprise a copolymer containing, by weight in the copolymer molecule, from 75 to acrylonitriie and from 1 to 25% of at least one other substance which contains the C=C linkage and which is copolymerizable with acrylonitrile.

13. A process as in claim 11, wherein the fibers comprise a blend of an acrylonitrile polymer containing, by weight in the polymer molecule, from 75 to of acrylonitrile and from 0 to 25% of at least one other substance which contains the C=C linkage and which is copolymerizable with acrylonitrile, with from 2 to 50% on the weight of the blend of a modifying polymeric material which is soluble in dimethylacetamide and which when mixed with the base polymer in an amount of from 2 to 50% by weight, results in a blend which forms a solution of at least 5% concentration in dimethylacetamide, which solution can be formed into fibers by conventional procedures.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,090,669 Dreyfus et a1 Aug. 24, 1937 2,157,117 Miles May 9, 1939 2,197,896 Miles Apr. 23, 1940 2,311,174 Hitt Feb. 16, 1943 2,394,165 Getaz Feb. 5, 1946 2,505,618 Hammerle Apr. 25, 1950 2,514,557 Pfau July 11, 1950 2,575,781 Barach Nov. 20, 1951 OTHER REFERENCES Sherman et al.: The New Fibers, 1946, published by D. Van Nostrand Co., Inc., New York. 

1. A PROCESS FOR PRODUCING CRIMPED, STABILIZED FIBERS COMPRISING AN ACRYLONITRILE POLYMER CONTAINING, BY WEIGHT IN THE POLYMER MOLECULE, AT LEAST 75 PERCENT OF ACRYLONITRILE, WHICH COMPRISES CONTINUOUSLY PASSING CONTINUOUS INTERNALLY STRAINED FIBERS COMPRISING THE POLYMER THROUGH A ZONE, HEATING THE FIBERS IN THE ZONE AND STRETCHING THE FIBERS IN THE ZONE AT LEAST 100 PERCENT WHILE THEY ARE UNDER THE INFLUENCE OF THE HEAT CONTINUOUSLY PASSING THE STRETCHED, ORIENTED FIBERS FROM THE ZONE INTO AND THROUGH A CRIMPING ZONE, CONTINUOUSLY FOLDING THE BUNDLE BACK AND FORTH UPON ITSELF IN A PACKED CONDITION IN THE CRIMPING ZONE TO THEREBY CRIMP THE FIBERS, CONTINUOUSLY TREATING THE PACKED BUNDLE OF FIBERS PASSING THROUGH THE CRIMPING ZONE WITH STEAM TO THEREBY HEAT THE FIBERS TO AT LEAST 100* C. AND RELAX THE INTERNAL STRAINS, REDUCE THE RESIDUAL SHRINKAGE CAPACITY OF THE FIBERS TO NOT MORE THAN 3 PERCENT AT 100* C., AND STABILIZIE THE RELAXED FIBERS IN THE CRIMPED CONDITION, AND CONTINUOUSLY REMOVING THE STABILIZED, CRIMPED FIBERS FROM THE CRIMPING ZONE. 